Hydrogenation of nitroparaffins

ABSTRACT

A PROCESS FOR THE CATALYTIC HHYDROGENATION OF SECONDARY MONO-NITROPARAFFINS WHEREIN HIGH CONVERSION AND SELECTIVITY TO SECONDARY ALKYL PRIMARY AMINES IS OBTAINED BY PASSING THE NITROPARAFFIN THROUGH A CATALYST BED AND HY DROGENATING AT AN AVERAGE CONVERSION TEMPERATURE OF 200 TO 450*F. WHERE THE DIFFERENCE IN *F. ($T) BETWEEN THE MAXIMUM CONVERSION TEMPERATURE AND THE INLET TEMPERATURE OF SAID BED IS AT LEAST 10*F.

United States Patent Office 3,739,027 Patented June 12, 1973 3,739,027 HYDROGENATION F NITROPARAFFINS Walter C. Gates, Jr., Newburgh, N.Y., assignor to Texaco Inc., New York, N.Y.

N0 Drawing. Filed May 21, 1971, Ser. No. 145,873 Int. Cl. (10% 85/10 US. Cl. 260-583 M 10 Claims ABSTRACT OF THE DISCLOSURE A process for the catalytic hydrogenation of secondary mono-nitroparafiins wherein high conversion and selectivity to secondary alkyl primary amines is obtained by passing the nitroparatfin through a catalyst bed and hydrogenating at an average conversion temperature of 2-00 to 450 F. where the difference in F. (AT) between the maximum conversion temperature and the inlet temperature of said bed is at least 100 F.

BACKGROUND OF THE INVENTION This invention relates to the production of amines and more particularly to the production of secondary alkyl primary amines having from 6 to 25 carbon atoms from secondary mono-nitroparafiins.

Primary amines have been prepared by initially nitrating paraffins'with nitric acid or nitrogen dioxide and subsequently reducng the nitroparafiin in the presence of a hydrogenation catalyst. Well known hydrogenation catalysts include members of Group IB alone or in combination with Group VI-B such as copper-chromite and Group VIII metals and compounds such as cobalt, nickel, platinum, palladium, and rhodium and their use has been suggested in reducing organonitrocompounds to corresponding amino compounds.

-In the hydrogenation of nitroparatlins to primary amines low temperatures of from 100 to 450 F. and preferably 200 to 400 F. have previously been employed. The reduction over a hydrogenation catalyst to primary amines is an exothermic reaction such that the formation of secondary amines increases at a substantial rate at temperatures above 450 F. To selectively convert to primary amines, low temperatures have been found to be essential and the exothermic reaction has been controlled by operating nearly isothermally in relatively dilute organic mediums such as n-parafiins. While nearly isothermal operations, i.e., operations within a narrow temperature range of 50 F. and less within the range set out above, overcomes to some degree the propensity to form secondary alkyl secondary amines and improves somewhat the selectivity of the reaction to primary amines, such conditions neverthless interfere with maximum conversion of the nitroparaffin to the primary amine.

It is therefore an object of this invention to provide a process for converting nitroparafiins to secondary alkyl primary amines.

Another object of this invention is to provide a process for selectively converting mono-nitroparafl'ins to secondary alkyl primary amines in high yields.

Other objects and advantages will become apparent from a reading of the following detailed description of the invention.

SUMMARY OF THE INVENTION Broadly, this invention contemplates a process for the catalytic hydrogenation of a secondary mono-nitroparaffin wherein hydrogen and nitroparaflin flow through a hydrogenation catalyst bed under conditions effective to convert said nitroparaflin to a secondary alkyl primary amine, the improvement which comprises passing said nitroparaflin through said catalyst bed at an average conversion temperature of from 200 to 450 F. and maintaining a difference of at least 100 F. between the maximum conversion temperature in said bed and inlet temperature of said bed.

More specifically, the difference (AT) between the maximum conversion temperature and the conversion temperautre at the inlet is at least 100 F. and up to 400 F. and preferably AT is from 150 to 300 F. This difference, AT, is effectively maintained by operating at inlet temperatures of from 100 to 400 F., preferably 150 to 250 F. and up to a maximum conversion temperature of 500 F. Temperatures above 500 F. adversely affect the process in that nitrogen is lost most probably as NH from the cracking off of the amine group. When the inlet temeprature contemplated is, for example, 100 F. a AT of at least 200 F. is employed so as to provide an average conversion temperature of 200 F. The designated inlet temperature is attained by introducing the nitroparaflin feed at a temperature of from 100 to 400 F. to the catalyst bed. The average conversion temperature, herein defined as the average temperature in F. of the inlet conversion temperature and the maximum conversion temperature, of from 200 to 450 F. and a AT of at least 100 and up to 400 F. can be attained in several ways. For example, the reactor can be composed of a plurality of small diameter catalyst tubes immersed in a fluid medium, including gases or liquids, which can transfer heat to or from the conversion zone. A reactor of large diameter may contain elements such as coils which permit the addition or extraction of heat as needed or the reactor can be composed of a multiplicity of sections with heat transfer zones between each section. Any of the aforementioned reactor means permit control over the average conversion temperature, AT and maximum conversion temperature. Reactor outlet temperatures never exceed and are generally lower than the maximum conversion temperature.

The instant invention contemplates a continuous process for producing secondary alkyl primary amines by reacting mono-nitroparaffins having from 6 to 25 carbon atoms with hydrogen. Mono-nitroparaflins encompassed within this process constitute secondary nirtro-nparafiins in which the nitro group is randomly positioned along the carbon chain on other than a terminal carbon atom. Illustrative mono-nitroparaffins include 2 or 3- nitrohexane, 2, 3 or 4-nitroheptane, 2, 3 or 4-nitrooctane, 2, 3, 4 or 5-nitrodecane, 2, 3, 4, 5 or 6-nitroundecane, 2, 3, 4, 5 or 6-nitrododecane, 2, 3, 4, 5, 6 or 7-nitrotridecane, 2, 3, 4, 5, 6 or 7-nitrotetradecane, 2, 3, 4, 5, 6,

7, 8 or 9-nitrooctadecane and mixtures thereof, for example, mixtures of G -C nitroparafiins. Such mono-nitroparaffins are provided by contacting a C C paraflin hydrocarbon, preferably a straight chain hydrocarbon, in a liquid phase with a vaporous nitrating agent illustrated by nitrogen dioxide or nitric acid at a temperature ranging from about 250 to 500 F. and pressures of from 1 to 20 atmospheres.

The illustrative nitration reaction briefly outlined above is generally permitted to proceed until about 5 to 50 percent of the paraffin has. been converted yielding a crude nitrated product of about 5 to 45 percent of mononitroparaffin and to 50 percent of unreacted paraffin along with lesser amounts of C C ketone, alcohol, carboxylic acid and polyfunctionals. Preferably, nitration to 10 to 25 weight percent nitroparaflin is undertaken. The mononitroparafiin so prepared may if desired be separated and recovered from the crude product as by distillation and subsequently hydrogenated to the corresponding amine, the reaction conveniently undertaken in the presence of a C -C parafiin hydrocarbon diluent. Alternatively, crude material comprising up to about 25 weight percent nitroparafiin may be hydrogenated directly wherein the unreacted paraffin constitutes the reaction medium. The crude nitrated product may also be caustic washed with for example sodium bicarbonate, ammonium hydroxide, sodium hydroxide or potassium hydroxide to remove acid by-products following nitration and prior to hydrogenation. Where the nitroparafiin feedstock is provided substantially free of acid by-products or contaminants neutralization may be omitted. Irrespective of whether caustic treatment is provided the feed introduced to the catalyst bed comprises from about 5 to 25 weight percent nitroparalfin in a C -C paraffin hydrocarbon diluent.

The nitroparaffin stream is introduced at an inlet temperature of from 100 to 400 F. to a bed of hydrogenation catalyst along with hydrogen under conditions such that at least 80 weight percent and preferably at least 90 weight percent of the nitroparafiin is selectively converted to at least 90 weight percent primary amine. Conversion conditions in the reactor containing the hydrogenation catalyst in addition to the reactor inlet temperature, maximum temperature and AT include liquid hourly space velocities of from 0.5 to 20 liquid volumes of nitroparaffin per volume of catalyst per hour and particularly space velocities of from 1.0 to 4.0 v./ v./ hr. The selectivity of the process to primary amine is dependent upon the relationship between the average conversion temperature, AT and the space velocity heretofore recited. In general, at low average temperature and at constant AT, low space velocities are employed to maintain a high level of conversion along with high selectivity. Similarly, at progressively higher average temperatures correspondingly high values for AT are preferably employed. Further, conversion is undertaken at mole ratios of hydrogen to nitroparaifin ranging from about 2.4:1 to 7.0:1 and preferably from 3 :1 to 4:1 under hydrogen pressures of from 200 to 1500 p.s.i.g.

The process described above can be conducted in the presence of conventional and well known hydrogenation catalysts comprising by way of illustration members of Groups I-B, VIB, VIIB and VIII of the Periodic Table. Illustrative of a Group I-B member is copper employed alone or in combination with a Group VI-B member such as copper chromite. As Group VI-B members I mention chromium, molybdenum and tungsten and combinations thereof and as a Group VII-B member rhenium. Group VIII members include platinum, palladium, rhodium, ruthenium, nickel and cobalt. The members may be present as the metal or compound thereof. As is known to the art, the members may also be supported on such bases as silica, kieselguhr or alumina. Preferred catalysts comprise supported catalysts comprising members of Group VII-B and VIII including rhenium, platinum, palladium, rhodium, and ruthenium where the metal is present in an amount of from 0.5 to 2.0 weight percent. A particularly preferred catalyst is palladium on a support of carbon.

Conventional recovery procedures may be employed in recovering the amine as by distilling the hydrogenated product by stepwise fractionation. Alternatively, the amine may first be converted and recovered as an amine salt by reaction with an inorganic acid followed by further treatment of the amine salt with alkali and thereafter recovering the primary amine by distillation. Amines produced according to this process may be employed as mold release agents, emulsion freeze-thaw stabilizers, pigment dispersing agents, polyurethan catalysts and anticaking anti-dusting agents. Their uses are also indicated as corrosion inhibitors, deleterious bacteria control agents, sludge dispersants and as detergents and de-icers in gasolines.

In order to more fully illustrate the nature of this invention and manner of practicing the same, the following examples are presented. In these examples the best mode contemplated for carrying out the invention is set forth.

4 Example I In the following experiments a hydrogenation reactor having an inside diameter of 1 inch was loaded with 61 grams of a conventional and commercially available nickel catalyst forming a bed 8 inches deep. A C -C feedstock composed of 14.5 weight percent mono-nitroparaffin, 82 weight percent n-paraffin, 1.5 weight percent ketone and 2 weight percent alcohols, nitrites, nitrates and difunctional paraffin saturated with ammonia at 50 to 75 p.s.i.g. was introduced at the rate of 67 grams per hour into the above reactor to effect the reduction of the nitroparaflin in the feedstock to the corresponding amine. Hydrogen at a pressure of from 550-600 p.s.i.g. was introduced into the bed of catalyst at the rate of 1-2 standard cubic feet per hour. Four experiments were conducted employing inlet temperatures varying from 360 to 214 F., maximum temperatures of from 380 to 223 F., average temperatures of from 370 to 219 F. and ATs of 20 and 9 F. Table I summarizes the results.

TABLE I Run A B O D Hours 25 25 25 25 Temperature, F

Inlet 360 310 264 214 MaximunL 380 330 273 223 Average. 370 320 269 219 AT 20 20 9 9 LHSV 1. 8 1. 8 1. 8 1. 8 mg. NHz/ 7.8 7.4 5.1 4.0 mg. NHag. 1.1 0.5 0. 5 0. 5 Conversion 91 76 50 36 Selectivity 78 88 93 100 As can be seen from Table I, the effiuent from Run A contained 7.8 mg. NH /g. and 1.1 mg. NH/g. corresponding to a conversion of 91 percent of the nitroparaffin to amine at a selectivity of 78 percent to primary amine. Decreasing the average temperature progressively in Runs B, C and D reduced the conversion progressively to 76, 50 and 36 perecnt while increasing the selectivity to primary amine to 88, 93 and 100 percent. In each run the value of AT showed the conversion to be undertaken at nearly isothermal operations and none of the runs achieved a conversion level of at least weight percent and a simultaneous selectivity of at least weight percent to primary amine.

Example II A hydrogenation reactor having an inside diameter of about 2 /2 inches was loaded with 2088 grams (1760 cc.) of the nickel catalyst employed in Example I composed of 50 weight percent nickel and 2 weight percent zirconium on kieselguhr to form a bed 36 inches deep. A C -C feedstock composed of 15.3 weight percent nitroparaffin, 81 weight percent n-parafiin, 1.5 weight percent ketone and 2 weight percent alcohols, nitrites, nitrates and difunctional paraffin was introduced to the reactor at a liquid hourly space velocity of 2.2 along with hydrogen flowing at the rate of 10 to 12 cubic feet per hour and a hydrogen pressure of 550 to 600 p.s.i.g. The feedstock was introduced to the reactor at an inlet temperature of 220 F., the maximum temperature of bed was 390 F., the average temperature being 305 F. and a AT of 170 F. The efiluent from the reactor contained 10.3 mg. NH /g. and 0.26 mg. NH/g. thus indicating that 93 percent of the nitroparafiin have been converted to amines with a selectivity to secondary alkyl primary amine of percent. As can be seen the beneficial effect of a AT of F. provided high selectivity and high conversion of mono-nitroparafiin to secondary alkyl primary amine.

Examples III A hydrogenation reactor having an inside diameter of about 2 /2 inches was loaded with 755 grams of the catalyst employed in Example II to form a bed 30 inches deep. A C -C feedstock composed of 14.1 weight percent nitroparaffin, 82 Weight percent n-parafiin, 1.5

weight percent ketone and 2 weight percent alcohols, nitrites, nitrates and difunctional parafiin was introduced at a liquid hourly space velocity 3.1 and at inlet temperatures ranging from 317 to 345 F. and at a maximum temperature of 362 F. The averag temperature during the run was 355 F. and the AT varied from 17 to 45 F. Hydrogen was introduced at the rate of to 12 cubic feet per hour and a hydrogen pressure of 550-600 p.s.i.g. was maintained. After 340 hours on stream the organic efliuent from the reactor contained 6.5 mg. NH /g. and 0.8 mg. NH/g. thus indicating that 77 percent of the nitroparaffin had been converted to amines with a selectivity to secondary alkyl primary amine of 80 percent. Comparing Example HI with Example II the benefical effect of maintaining at AT of at least 100 F., and in the instance 170 F. is shown.

Example IV A hydrogenation reactor having an inside diameter of about 2 /2 inches was loaded with 676 grams (1700 cc.) of a catalyst composed of 1 weight percent palladium on carbon to form a bed 18 inches deep. A C -C feedstock composed of about 14.2 weight percent nitroparaffin in about 83 weight percent n-parafiin was introduced to the reactor at a liquid hourly space velocity of 1.5 along with 9.1 cubic feet per hour of hydrogen at a hydrogen pressure of from 550-600 p.s.i.g. In a series of runs designated E through I the inlet temperature, maximum temperature, average temperature and AT were varied. Table II summarizes the results.

TABLE II Run E F G H I J Hours 1, 300 1, 225 1, 325 1,200 1, 250 1, 275 Temperature, F

Inlet 170 200 185 200 240 240 Maximum 325 320 370 370 365 410 Average 257 260 277 285 302 325 AI 155 120 185 170 125 170 mg. NHz/g 9. e 9. 4 10. 4 10. 2 10. 5 10. 3 mg. NH/g 0. 20 0. 24 0. 28 0. 28 0. 33 0. 48 Conversion. 91 89 100 96 100 100 Selectivity 98 98 97 97 97 95 From Runs B through I the advantage of operating with a large AT is seen providing high conversion and high selectivity to secondary alkyl primary amines.

Example V A hydrogenation reactor having an inside diameter of about 2 /2 inches was loaded with 680 grams (1580 cc.) of a catalyst composed of 1 weight percent palladium on carbon to form a bed 19 inches deep. A feedstock composed of 12.7 weight percent C -C nitroparaflin, 83.8 weight percent C -C n-parafiin along with lesser amounts of ketones, alcohols, nitriles, nitrates and difunctional paraffin was introduced at the rate of 1770 grams per hour into the reactor corresponding to a liquid hour- 1y space velocity of 1.3. The reactor inlet temperature was 280 F. and the maximum temperature within the bed was recorded at 400 F. Hydrogen was introduced at'the rate of 10-12 cubic feet per hour at a pressure of 550-600 p.s.i.g. After 160 hours on stream the organic eflluent from the reactor contained 8.9 mg. NH /g. and 0.77 mg. NH/g. thereby indicating that 100 percent of the nitroparafiin had been converted to amines with a selectivity to secondary alkyl primary amine of 93 per- 6 cent. The average temperature of this run was 340 F. and AT was 120 F.

Example VI The hydrogenation reactor of the previous example was loaded with 1022 grams of a 1 percent palladium on carbon catalyst to form a bed 28 inches deep. The C -C nitroparaflin feedstock of Example V was introduced to the reactor at an inlet temperature of 235 F. and at a liquid hourly space velocity of 1.4. The maximum temperature within the bed was 404 F. corresponding to a AT of 169 F. and an average temperature of about 320 F. Hydrogen was introduced at the rate of 10-12 cubic feet per hour at a pressure of 550-600 p.s.i.g. After hours on stream the organic efiiuent from the reactor contained 10.4 mg. NH /g. and less than 0.4 mg. NH/g. thus indicating that percent of the nitroparaffin had been converted to amines with a selectivity to secondary alkyl primary amine of greater than 96 percent.

I claim:

1. In a process for the catalytic hydrogenation of a secondary mono-nitroparatfin having from 6 to 25 carbon atoms wherein hydrogen and nitroparaffin flow through a hydrogenation catalyst bed in the mole ratio of hydrogen to nitroparafiin of from about 2.4:1 to 7.0:1 and hydrogen pressures of from 200 to 1500 p.s.i.g., to convert said nitroparaflin to a secondary alkyl primary amine, the improvement which comprises passing said nitroparaflin through said catalyst bed at an inlet temperature of from 100 F. to 400 F., at an average conversion temperature of from 200 to 450 F. and up to a maximum conversion temperature of 500 F., and maintaining a AT of at least 100 F. increase in temperature between the maximum conversion temperature in said bed and the inlet temperature of said bed.

2. A process according to claim 1 wherein said inlet bed temperature is from to 250 F.

3. A process according to claim 1 wherein said nitroparaifn passes through said catalyst bed at a liquid hourly space velocity of from 0.5 to 20.

4. A process according to claim 1 wherein said nitroparaffin passes through said catalyst bed at a liquid hourly space velocity of from 1.0 to 4.0.

5. A process according to claim 1 wherein AT is from 100 to 400 F.

6. A process according to claim 1 wherein said AT is from 150 to 300 F.

7. A process according to claim 1 wherein the hydrogen to nitroparafiin mole ratio is from 3:1 to 4:1.

8. A process according to claim 1 wherein said nitroparaflin has from 10-14 carbon atoms.

9. A process according to claim 1 wherein said nitroparaflin comprises a mixture of C C nitroparafiins.

10. A process according to claim 1 wherein said nitroparaffin passes through said catalyst bed in admixture with a C -C parafiin hydrocarbon and where said nitroparatlin comprises from about 5 to 25 weight percent of said mixture.

References Cited UNITED STATES PATENTS 3,470,250 9/ 1969 Patterson et a1. 260-583 M 3,485,875 12/1969 Menapace 260583 M 2,174,498 9/1949 Johnson 260-583 M JOSEPH P. BRUST, Primary Examiner W3 5 E v UNITED STATES PATENT OFFICE QERTIFICATE OF CORRECTION N 3,739,027 Dated 6/12/73 Inventor) Walter C. Gates, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ai '1 J Col.3, line 29 "temperature" should read --temperatures Col. 4, Table l, line 28 "mg NH should read Col. 4, line 38 "perecnt" should read -Derc ent- Col. 5, line 5 "averag" should read W -average Col. 5, line 55 "nitriles" should read --nitrites- Signed and sealed this 1st day of January 1974 (SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

